This disclosure describes apparatus for performing containerless material processing of both conducting and nonconducting materials on earth and in the low gravity of space. The apparatus maintains the material at a fixed levitation node, in a stable manner, without physical or electromagnetic support, in a gas filled volume. This disclosure describes the method of levitating materials by aerodynamic forces created by gas flowing through an enclosed volume. The enclosed volume contains a convergent-divergent section. The duct cross-section is either circular or rectangular. Spheres and right circular cylinders can be levitated by a conduit having circular cross-section while cylinders can be levitated in a stable manner by a conduit having a rectangular cross-section.
Heretofore, a column of gas has been utilized to support objects during scientific research for example, the growth of a drop of water supported by the upward flow of a cloud has been studied in a vertical tapered tube. The water drop was held stationary in the tube by varying the upward velocity of the air flow until the drag forces on the sphere equalled the drop weight. Airplane spin characteristics have been studied using free falling scale models in a vertical air column. Very small uranium spheres have been levitated in argon/flourine gas, above 1400K, using a vertical jet comprised of a central jet tube surrounded by multiple equally spaced jets of the same diameter All jets exhausted into a funnel shaped nozzle and an electromagnetic field was used to maintain stability.
These examples of single, vertical jets, become unstable when the jet axis is tilted so that the object center of gravity is no longer colinear with the jet axis.
Other attempts to provide containerless processing of materials using air jets has included several individual jets placed at equal spherical angles impinging on a central material object.
On earth, metal samples for metallurgical anaylsis are melted without a container while suspended and heated by a high frequency electric field. This technique is being extended to space processing because it is not gravity dependent.
Apparatus for shaping and enhancing acoustical levitation forces is illustrated in U.S. Pat. No. 4,218,921. High power acoustic fields provide levitation forces adequate to position small spheres of material in space. Interest in acoustic levitation has been stimulated by potential space applications but does not have a history of wide usage in earth laboratories.
Acoustic levitation in liquids can be accomplished on earth by establishing standing waves in a column of liquid. A droplet of another liquid, immiscible in the column liquid will position itself in a stable manner near a pressure node, when an acoustic transducer establishes a high intensity sound field. However, levitation of fluids in an immiscible fluid is not a technique useful in containerless processing.
The prior art for earth applications, utilizing a single jet, are gravity dependent for positioning and are not applicable to low gravity operation.
This disclosure describes a gas levitator which will support the material as the levitator axis is rotated from vertical to horizontal, to inverted, to vertical. This levitator can be used on earth at any angle of inclination with respect to an earth reference and in space.
In addition, none of the prior levitation devices have demonstrated the capability of containerlessly processing non-conducting material at high temperature (i.e., .gtoreq.800.degree. C.). The materials which have been successfully processed were conductors only. Electromagnetic coil assemblies have been required to provide stable levitation of the melt.
Accordingly, an important object of the present invention is to provide an apparatus for positioning a material specimen in a containerless environment for processing on earth and in low gravity environments.
Another important object of the present invention is to provide a simple apparatus for levitating a specimen by means of a gas which will operate in any orientation and is not gravity dependent.
Still another important object of the present invention is to provide a gas levitator device which will operate in any orientation and provides a stable positioning of the specimen.
Another important object of the present invention is to provide a gas levitator device which will operate over a broad temperature range.
Another important object of the invention is to provide apparatus for levitating a specimen in a gas which will operate for conductors and non-conductors as well.